In recent years, in order to form a deep groove trench structure or a through hole having a high aspect ratio (a depth of a through hole/an opening diameter of a through hole) in a semiconductor substrate using a dry etching method, a plasma processing device including an opposite electrode formed from a helical antenna structure has been widely used (for example, Patent Literature 1).
FIG. 5A and FIG. 5B are SEM pictures showing a cross-sectional shape of a non-through hole that is formed by applying AC voltages of different frequencies to an opposite electrode. FIG. 5A is the SEM picture when a frequency is 13.56 MHz and FIG. 5B is the SEM picture when a frequency is 2 MHz. Both FIG. 5A and FIG. 5B show results obtained by performing an etching process such that a diameter of a hole becomes 10 μm. It can be understood that deeper etching is possible, a variation of an inner diameter in the vicinity of an opening portion is smaller, and a more favorable hole shape is obtained in a case in which a frequency is 2 MHz (FIG. 5B) than a case in which a frequency is 13.56 MHz (FIG. 5A).
FIG. 6 is a graph showing spectroscopic measurement results of light emission of plasma generated when AC voltages of different frequencies are applied to an opposite electrode. The horizontal axis represents applied power [W] and the vertical axis represents an F radical light emission intensity. Here, “F radical” refers to a particle that is observed in plasma generated when a fluorine (F)-containing process gas is used. The following points are clarified based on the graph of FIG. 6. FIG. 6 shows results obtained when the plasma processing device of FIG. 7 is used. While FIG. 7 shows a configuration example in which a frequency of an AC power supply is 2 MHz, when an AC power supply whose frequency is 13.56 MHz is used, an AC power supply is replaced at the same position, and thus the results shown in FIG. 6 are obtained.
When a frequency is 2 MHz (the mark □), an electric discharge region transitions from a region whose F radical light emission intensity is low (a glow discharge region) to a region whose F radical light emission intensity is high (an inductive discharge region) according to an increase of applied power. In this case, there is a mode jump region in which discharge is switched between the two regions. Due to the mode jump region, there is a problem in that a manual adjustment time for about 1 minute is necessary in the inductive discharge region until the discharge is stabilized.
On the other hand, when a frequency is 13.56 MHz (the mark o), there is no mode jump region that is observed when the frequency is 2 MHz. Therefore, even if applied power increases and decreases, discharge is stably maintained and stable etching is possible. However, when the frequency is 13.56 MHz, an F radical light emission intensity is about half that of the inductive discharge region when the frequency is 2 MHz. Accordingly, there is a problem of an etching speed being halved and a processing time being doubled compared with a case when the frequency is 2 MHz.
The development of a plasma processing device having two advantages of enabling etching using an inductive discharge region in which “F radical” is significantly observed and enabling to avoid an influence of a mode jump region is expected.